In this French Patent No. 02 09176, with reference to FIG. 1, FIG. 2 and FIG. 3, the current method that is most commonly used by the motorcycle manufacturers to produce the attachment of the front wheel assembly is disclosed. FIG. 1 shows a sketch of the front wheel assembly of a motorcycle made in the median plane of the latter. FIG. 2 shows the same sketch but seen from the front. FIG. 3 shows the detailed assembly of the steering column via a section 1-1 of FIG. 2 passing through its axis of rotation. Thus, the front wheel (1) is, in the vast majority of designs, held by the front suspension element that consists of two parallel and telescopic struts (2a) and (2b), ensuring the functions of guiding, suspension and absorbing shocks, and located on both sides of the wheel, on its axis of rotation and perpendicular to the latter. These two elements are connected in their upper portion by two plates. An upper plate (3) is located at their upper end, and a lower plate (4) is located below the upper plate and at a distance that allows total freedom of movement of the wheel in its oscillations. These two plates encircle the steering column of the chassis.
The steering column is the front portion of the chassis. It consists of a head (5) into which guiding means (6a) and (6b), which allow the pivoting of a shaft (7) that passes through them along the shaft of the head (5), are located at each end. This shaft (7) is called a “steering column shaft.” It is attached to the middle of the lower plate (4), passes through the steering column of the chassis by passing into the guiding means (6a) and (6b), then passes through the upper plate (3).
A pivoting function is thus created between the chassis and the front wheel assembly. With the handlebars (8) that are attached to the upper plate (3), the pilot can change direction by making the front wheel assembly—and therefore the front wheel—pivot.
FIG. 3 shows a commonly used design, by way of nonlimiting example, of an assembly of the steering column. Here, the guide means (6a) and (6b) are shown by roller bearings with conical rollers, mounted clamped in the housings of the column (5), facing one another and in an O shape. The nut (9) makes it possible to regulate the play necessary to the rotation of the roller bearings. The checknut (10) locks the overall device by preserving this operational play.
So as to give stability to the vehicle, the pivoting shaft is tilted toward the front so that the axis of rotation of the front wheel is found in front of the steering column. The angle (A) that is formed by the perpendicular line to the ground and the pivoting axis is called a “caster angle.” The distance (C) between the projection of the pivoting axis on the ground and the point where the wheel makes contact with the ground is called “ground castor.”
In the French Patent No. 02 09176, the importance of the value of the caster angle and the desire of the users, in particular in competition, to be able to quickly modify the value of this angle, is also explained.
The invention according to the French Patent No. 02 09176 proposes an upper and lower plate assembly and a column shaft that can be mounted easily on the column (5) of the motorcycle chassis that are used in series by the manufacturers, which offers the special feature of being able to vary the caster angle (A) by a value that is more or less on the order of 1° to 3° and the offset (B), independently, on the upper and lower plates, whereby these adjustment modifications can be carried out quickly without detaching the front wheel assembly.
Thus, in referring to FIG. 4, FIG. 5, FIG. 6, FIG. 7 and FIG. 8, an embodiment of the invention is disclosed according to the French Patent No. 02 09176. FIG. 4 is a section 1-1 of FIG. 2 for mounting the steering column allowing the adjustment of the caster angle (A) in the center position. FIG. 5 is a section H-II of FIG. 4. FIG. 6 is a section that is identical to FIG. 4 but in an end adjustment position. FIG. 7 is a section along IfI-III of FIG. 4. FIG. 8 is the enlarged aspect IV of surfaces (20) and (21). In this assembly, the steering head (5) of the chassis is preserved, but the guiding elements (6a) and (6b) of FIG. 3, ensuring the pivoting of the front wheel assembly relative to the chassis, are replaced respectively by the elements (16) and (11) that are located respectively in the upper plate (33) and the lower plate (34). In this way, the rotation of the front wheel assembly is preserved despite the locking in rotation of the column shaft (37).
The shaft (37) passes through the guide element (11) that is shown here by way of nonlimiting example by a roller bearing with a double row of balls and attached in a suitable manner in the plate (34) like, for example, in a non-limiting way, a shrunk-on fitting and machined support, so as to support the axial forces directed upward and transmitted by the front wheel assembly through the plate (34), and passes through a ball joint with oblique contact (12) located at the site of the guide element (6b) of FIG. 3 in the head (5) in a suitable way and able to support the axial forces transmitted by the element (11).
A crosspiece (24) can be located between the elements (11) and (12) so as to ensure minimum space between the top of the plate (34) and the bottom of the head (5) to allow the rocking movement of the plate (34). This crosspiece (24) can also be provided with any sealing means to protect the elements (11) and (12).
In its upper portion, the shaft (37) passes through a guide part (14) that is attached at the site of the element (6a) of FIG. 3 in the head (5) in a suitable manner and by way of nonlimiting example by a shrunk-on fitting and a float-needle screw (13) inhibiting any movement of rotation of the part (14) in the head (5). The part (14) has a groove with parallel sides (18a) and (18b). It is imperative that the axis of this groove be located in the plane of FIG. 4, or more exactly in the plane of FIG. 1, which is the median plane of the vehicle and the plane of definition of the caster angle (A).
Two flat surfaces with parallel sides (19a) and (19b) with dimensions that allow their sliding without play on the sides respectively (18a) and (18b) of the groove of the part (14) are produced on the shaft (37).
The upper surface (20) of the part (14) is a portion of the cylinder of the shaft (30) that is perpendicular to the sides (18a) and (18b) of the groove and that pass through the center of rotation of the ball joint (12). The part (15) that is located above the part (14) has a cylindrical lower surface (21) that is coupled to the surface (20) such that the part (15) can slide over the part (14) by pivoting around the axis (30) of cylindrical surfaces. The part (15) is pierced in its center and perpendicularly to the shaft (30) of the cylindrical surface to allow passage from the top of the column shaft (37).
The shaft (37) then passes through the guide element (16), shown here by way of nonlimiting example by a rigid roller bearing with balls, suitably attached in the upper plate (33) and in particular by a shrunk-on fitting and holding circlips (17), and passes through the crosspiece (22) on which a locking nut (23) rests.
When the nut (23) is not tight, it is possible to make the front wheel assembly pivot around the shaft (30), guided by the sliding of the sides (19a) and (19b) of the shaft (37) on the sides (18a) and (18b) of the groove of the part (14) and the sliding of the cylindrical surface (21) from the part (15) to the conjugated surface (20) of the part (14). Once positioned at the value (E) of the FIG. 6 corresponding to the desired value of the modification of the caster angle (A), the nut (23) is tightened in a suitable manner to lock this position by adhesion of surfaces (20) and (21).
To ensure an effective locking and to avoid any risk of sliding of the surface (21) over the surface (20), subjected to significant forces transmitted by the front wheel assembly in the braking phase or strong compression of the suspension, it is advantageous to provide locking by a stop and not by adhesion alone by making small grooves on the surfaces so that the surface (21) engages perfectly with the surface (20) as shown in FIG. 8. These grooves are made on lines parallel to the shaft (30) of the cylindrical surfaces (20) and (21). They are shown here by way of nonlimiting example of a triangular section and allow an angular adjustment by pitch (a). So as to provide modifications that are sensitive to the behavior of the vehicle, it is recommended to produce a pitch (a) on the order of 0.2°. A pitch of a more significant value limits the number of usable catches because it causes modifications of the behavior of the front wheel assembly that are too pronounced from one catch to the next. The use in competition of the invention according to the French Patent No. 02 09176 shows that the adjustments of more than the order of 1° are never used. A pitch on the order of 0.2° makes it possible to obtain on the order of 5 adjustment catches that are more or less usable relative to the original position, which shows a good adjustment range.
To comply with the catches on the order of 0.2°, it is necessary to produce a very small cog that becomes difficult to handle and that is primarily vulnerable if it is not positioned properly before the nut (23) is tightened. In addition, these cogs make the parts (14) and (15) very expensive to produce.